The present invention pertains to the radio communication art and, more particularly, to an improved radio blanker inhibit circuit.
Blanker circuits, and means for inhibiting the same, are well known in the radio communication art. Commonly, the blanker includes a noise sampling channel and a blanking gate, which gate is in series with the radio processed signal and, prior to a narrow selectivity stage which would otherwise "stretch" the noise pulses causing severe degradation. The noise sampling channel includes means to determine the presence of noise pulses, such as radiation from automobile ignition systems, on the input radio frequency signal and close the blanker gate during the occurrence of such noise pulses.
There are occasions in which operation of the blanker actually degrades the intelligibility of the processed signal. The prior art has developed circuitry to inhibit the blanker operation during two types of signal conditions. In the first, the blanker is inhibited when the repetition rate of the noise pulses exceed a fixed frequency. This is commonly known as rate shut-off.
It has also been known in the prior art to inhibit the blanker circuit when the magnitude of the receiver processed signal exceeds a predetermined threshold level. This is commonly referred to as level shut-off.
There are numerous instances, however, when operation of the blanker circuit degrades the intelligibility of the receiver's output even though either the repetition of the input noise interference is less than the rate shut-off threshold or the magnitude of the receiver processed signal is less than the level shut-off threshold. Thus, there has been a long felt need in the receiver blanker art for inhibit circuitry which inhibits blanker operation under all conditions in which the blanker actually degrades the receiver processed signal.